WBR0338

Author	[[PageAuthor::Yazan Daaboul, M.D. (Reviewed by Yazan Daaboul, M.D. and Alison Leibowitz [1])]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Physiology
Sub Category	SubCategory::Reproductive
Prompt	[[Prompt::A researcher studying the process of ovulation in human females recruits 10 female volunteers. He injects subcutaneously human chorionic gonadotropin (hCG) hormone and retrieves the eggs 35 hours later. Using the appropriate technique, he views the eggs under fluorescence microscopy. Under fluorescence microscopy, which of the following findings does the researcher most likely observe?]]
Answer A	AnswerA::Beginning of the disappearance of the nuclear envelope
Answer A Explanation	AnswerAExp::Early prophase I is characterized by the disappearance of the nuclear envelope.
Answer B	AnswerB::Alignment of the sister chromatids along the equatorial plate.
Answer B Explanation	AnswerBExp::Alignment of the sister chromatids along the equatorial plate occurs during metaphase II, the stage where oocyte arrest takes place following ovulation and prior to fertilization.
Answer C	AnswerC::Alignment of the homologous chromosomes along the equatorial plate
Answer C Explanation	AnswerCExp::Alignment of the homologous chromosomes along the equatorial plate occurs during metaphase I.
Answer D	AnswerD::Migration of sister chromatids to opposite poles
Answer D Explanation	AnswerDExp::Migration of sister chromatids to opposite poles occurs during anaphase II.
Answer E	AnswerE::Migration of homologous chromosomes to opposite poles
Answer E Explanation	AnswerEExp::Migration of homologous chromosomes to opposite poles occurs during anaphase I.
Right Answer	RightAnswer::B
Explanation	[[Explanation::The process described above is induction of ovulation, whereby patients typically receive subcutaneous injections of hCG (a mimicker of LH) followed by egg retrieval 35-40 hours later. In this process, ovulation most likely occurs, and retrieval of oocytes is then made possible. Typically in females, cell division of oocytes is arrested at metaphase II following ovulation and prior to fertilization. Only if fertilization occurs, will the oocyte resume meiosis II. Under fluorescence microscopy, metaphase II is characterized by the presence of sister chromatids along the equatorial plate. In contrast, metaphase I is characterized by the presence of homologous chromosomes along the equatorial plate. Unlike humans, other species may produce oocytes at different stages of meiosis. Educational Objective: Following ovulation, meiosis of human oocytes is arrested at metaphase II, which is a phase of cell division characterized by the presence of sister chromatids along the equatorial plate. References: First Aid 2014 page 569]]
Approved	Approved::Yes
Keyword	WBRKeyword::Metaphase I, WBRKeyword::Metaphase II, WBRKeyword::Anaphase, WBRKeyword::Oocyte, WBRKeyword::Egg, WBRKeyword::HCG, WBRKeyword::Human chorionic gonadotropin, WBRKeyword::Meiosis, WBRKeyword::Ovulation, WBRKeyword::Fertilization, WBRKeyword::Fluorescence microscopy
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